Inhalation anaesthetics

Question 1

What are some commonly used gas anaesthetics?

Answer 1

Isoflurane, Sevoflurarane, Methocyflurane, Desflurane, Halothane and nitrous oxide

Question 2

What physiological factors can effect the effectiveness of these?

Answer 2

Changes in CO and ventilation rate –> very minimal hepatic metabolism

Question 3

MOA?

Answer 3

Inhibition of glutamate receptors and increased GABA activity

Question 4

Factors that influence potency, rate of induction and recovery?

Answer 4

Inspired conc, alveolar ventilation and respiration, solubility in blood and other tissues, cardiac output - diffusion gradient, tissue perfusion and solubility in lipid, metabolism, intrinsic activity in the CNS

Question 5

What is MAC?

Answer 5

Minimum alveolar concentration

MAC(vol%) = alveolar conc. at 1atm producing immobility in 50% of the patients exposed to a painful stimulus

Question 6

How do you measure potency?

Answer 6

1/MAC

Question 7

What can decrease MAC and should they be given more or less of the drug?

Answer 7

Give less of the drug

Cause: hypothermia, hyponatremia, pregnancy, CNS depressants, anaemia and hypotension, hypoxia, respiratory acidosis

Question 8

What can increase MAC and should they be given more or less of the drug?

Answer 8

Give more of the drug

Cause: Hyperthermia, hypernatremia, CNS stimulants, decreased brain perfusion

Question 9

What are some of the effects of isoflurane?

Answer 9

Depresses respiratory drive and ventilatory responses
Myocardial depressant
Inhibits sympathetic baroreflex responses and may cause a reduction in systemic vascular resistance
Good muscle relaxant BUT potentiates non-depolarising neuromuscular junctions

Question 10

What characteristic does isoflurane not have which is an important anaesthetic requirement?

Answer 10

Doesnt have pain blocking properties the dog may appear to be under anaesthetic but the pain pathways are still communicating

Question 11

What can isoflurane prevent?

Answer 11

Seizures it has anticonvulsant properties

Question 12

What is the general use for isoflurane?

Answer 12

Mostly used for maintenance

Question 13

What is the metabolism of isoflurane like?

Answer 13

Undergoes minimal hepatic metabolism (0.2%)

Question 14

What receptors does Nitrous oxide target?

Answer 14

Has analgesic properties via NMDA receptors

Question 15

What is nitrous oxide usually used in combination with?

Answer 15

Used in combo with other agents (increased onset rate and decreased conc of more potent volatile anaesthetics)

Question 16

What can prolonged use of nitrous oxide cause?

Answer 16

Inhibits methionine synthetase, causes folate deficiency and bone marrow defects

Question 17

What are some adverse effect of nitrous oxide?

Answer 17

Cases of increased intracranial pressure (brain tumours)
Pneumothorax, gastric dilation or volvulus
Severe respiratory disease
Anaemic patients